Section 15. Sinking funds; how kept and invested; income therefrom and application thereof

The sinking funds provided for the payment of interest and the extinguishment of the principal of the debts of the state heretofore contracted shall be continued; they shall be separately kept and safely invested, and neither of them shall be appropriated or used in any manner other than for such payment and extinguishment as hereinafter provided. The comptroller shall each year appraise the securities held for investment in each of such funds at their fair market value not exceeding par. The comptroller shall then determine and certify to the legislature the amount of each of such funds and the amounts which, if thereafter annually contributed to each such fund, would, with the fund and with the accumulations thereon and upon the contributions thereto, computed at the rate of three per centum per annum, produce at the date of maturity the amount of the debt to retire which such fund was created, and the legislature shall thereupon appropriate as the contribution to each such fund for such year at least the amount thus certified.
If the income of any such fund in any year is more than a sum which, if annually added to such fund would, with the fund and its accumulations as aforesaid, retire the debt at maturity, the excess income may be applied to the interest on the debt for which the fund was created.
After any sinking fund shall equal in amount the debt for which it was created no further contribution shall be made thereto except to make good any losses ascertained at the annual appraisals above mentioned, and the income thereof shall be applied to the payment of the interest on such debt. Any excess in such income not required for the payment of interest may be applied to the general fund of the state.